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| News Items |
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| Toxic blue-green algae
at Rietvlei - 9 March 2007 |
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Friday’s
scorching
temperatures
have
resulted
in
the
Rietvlei
Wetland
Reserve
having
to
remain
closed
this
weekend,
due
to a
health
risk
caused
by a
toxic
blue-green
algae,
which
thrives
in
hot
weather.
The
blue-green
algal
bloom
poses
a
health
risk
to
recreational
users
of
the
water
body.
The
reserve
is
an
important
ecological
area
and
is
well
used
by
various
recreational
groups.
Cliff
Dorse,
of
the
City’s
Biodiversity
Management
Branch,
says
the
unicellular
algae
combine
into
small
colonies
and
these
can
be
seen
as
little
green
specks
in
the
water
column.
The
algae
wash
up
on
the
shore
line
and
collect
in
the
shallows,
depending
on
which
way
the
wind
is
blowing.
“In
such
areas
it
can
become
so
dense
that
it
forms
a
thick
layer
of
yellowish-green
scum.
It
is
in
such
areas
that
the
toxin
concentrations
are
potentially
at
their
highest,”
says
Dorse.
The
presence
of
the
algae
was
identified
last
Friday
and
a
monitoring
programme
was
initiated.
The
results
from
yesterday
(Thursday)
morning’s
sample
appeared
very
promising
and
it
looked
likely
that
the
vlei
would
be
open
for
the
weekend.
“Unfortunately
Friday’s
very
hot
weather
was
perfectly
suited
to
the
exponential
growth
of
the
algae.
This
resulted
in
an
explosion
in
algal
activity
and
numbers
and
the
decision
was
made
to
keep
the
water
body
closed
this
weekend,”
says
Dorse.
He
added
this
was
a
precautionary
measure
and
the
vlei
would
be
re-opened
as
soon
as
further
laboratory
analysis
had
shown
that
the
water
was
fit
for
use.
Additional
water
samples
will
be
collected
throughout
next
week
in
an
effort
to
get
a
clear
understanding
of
the
fluctuations
of
the
algae.
A
large
number
of
City
departments,
including
Environmental
Health,
Roads
and
Stormwater
and
Scientific
Services
have
been
involved
in
advising
the
City’s
Biodiversity
Management
Branch
on
what
actions
to
take.
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[continued
on
next
page] |
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Rietvlei
was
in
the
news
in
December
2006
when
80
tons
of
fish
died,
probably
as a
result
of a
lack
of
oxygen.
Although
it
is
not
yet
known
if
blue-green
algae
were
a
factor,
the
two
environmental
phenomena
may
be
connected.
“A
healthy
functioning
Rietvlei
is
an
essential
goal,
both
for
the
environment
and
to
preserve
and
enhance
the
invaluable
recreational
asset
which
it
provides,”
says
Dorse.
The
next
pages
have
some
pictures
of
blue-green
algae
on
Rietvlei.
The
Toxic
Algae
Fact
Sheet
(accessible
from
the
News
Page)
provides
more
information
about
blue-green
algae. |
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Blue-green
algae
in
water
close
to
shore
of
north
vlei. |
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A
rich
pea-soup
green
growth.
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Blue-green
algae
washing
up
on
shoreline.
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